I have another explanation: if is not self-custody is just an account. In order to retrieve the access to those sats you need to login with user/pwd or whatever other method for an account, provided by the owner of the keys.

Bitcoin in self-custody it doesn't use "login" or accounts, it just use wallets, with private keys.

Account = you depend of somebody else to provide the keys Wallet = you manage it yourself, with your own keys

Also there's no such thing as "bitcoin in custody of somebody else"... that is just an IOU. That's why I think is better to refer as "account".